This invention relates to a front wheel drive clutch for tractors. More particularly, the present invention relates to a front wheel drive clutch provided in a front wheel drive system which is branched from an intermediate position of a rear wheel drive system including left and right brakes for braking left and right rear wheels.
When the above-referenced front wheel drive clutch is structured such that it is engaged by the action of a spring while it is disengaged by the action of fluid pressure, the clutch is normally engaged so as to drive the front wheels together with the rear wheels so that the braking force by the left and right brakes is applied also to the front wheels. Thus, even when an engine shutdown or a trouble with respect to the fluid supply system is caused during the running of tractor, free running distance of the vehicle can be shortened by actuating the brakes.
JP, A No. 59-192619 discloses a front wheel drive clutch of the above-referenced type together with a front wheel drive clutch which is engaged by the action of fluid pressure and is disengaged by the action of a spring. The front wheel drive clutch engaged by the action of a spring and disengaged by the action of fluid pressure comprises a clutch housing which is fixedly mounted on a transmission shaft for transmitting power to the front wheels, a drive gear which is rotatably mounted on the transmission shaft and has a boss portion extending into the clutch housing, a plurality of one and the other frictional elements which are slidably but non-rotatably supported respectively by the clutch housing and by the boss portion of drive gear, a slidable cylinder member which is disposed within the clutch housing at one side of the frictional elements, plural leaf springs which are disposed within the clutch housing in series with the slidable cylinder member so as to bias the cylinder member to move in a direction of causing the engagement of frictional elements, a non-slidable piston which is disposed within the slidable cylinder member, and a fluid passage which is perforated in the transmission shaft so as to open into a fluid chamber defined between the slidable cylinder member and non-slidable piston such that the cylinder member is moved away from the frictional elements by fluid pressure applied to the fluid chamber. Thus, the front wheel drive clutch is engaged by the force of leaf springs, which causes the engagement of frictional elements through the movable cylinder member, and is disengaged by fluid pressure which acts upon the cylinder member so as to move away from the frictional elements. This clutch is very lengthy because the plurality of frictional elements, the slidable cylinder member and the leaf springs are arranged in series within the clutch housing. The clutch is also expensive because number of parts including the plurality of frictional elements is large.
JP, U No. 52-103252 discloses a claw clutch which is disposed between coaxially arranged two transmission shafts and which is engaged by the action of a spring and is disengaged by the action of fluid pressure. The claw clutch comprises, within a clutch casing, a fixed clutch member which is fixedly mounted on a transmission shaft of the driven side and has integral driven teeth, a movable clutch member which is slidably but non-rotatably mounted on a transmission shaft of the drive side and has integral drive teeth engageable with the driven teeth, a coil spring which is arranged in series with the movable clutch member and acts upon the movable clutch member to move into a direction of causing the engagement of drive teeth with the driven teeth, a cylinder member which is secured to the clutch casing and by which the movable clutch member is slidably received in a fluid-tight manner through a plurality of seal rings, and a pipe which extends through the clutch casing and opens into the cylinder member such that the movable clutch member is moved into a direction of causing the disengagement of drive teeth from the driven teeth by fluid pressure applied to the movable clutch member through the pipe. This claw clutch is lengthy because the movable clutch member and the coil spring are arranged in series. The claw clutch is particularly poor in durability because the movable clutch member is rotated in contact with the fixed cylinder member so that the seal rings between these members will be damaged with the use of claw clutch.
A primary object of the present invention is to provide a novel front wheel drive clutch of the type engaged by the action of a spring and disengaged by the action of fluid pressure which is small in the number of parts so as to be inexpensive, which is compactly designed in the axial length of clutch, and which is rich in durability because of the absence of relatively rotated two members damaging the fluid tightness.
An attendant object is to provide a novel front wheel drive clutch which is easy in assembling.
In a tractor comprising a rear wheel drive system which includes left and right brakes (28) for braking left and right rear wheels, the present invention relates to a front wheel drive clutch (38) provided in a front wheel drive system which is branched from an intermediate position of the rear wheel drive system. According to the present invention, the front wheel drive clutch comprises:
drive teeth (37a) integral with a drive gear (37) which is rotatably mounted on a transmission shaft (36) for transmitting power to the front wheels;
driven teeth (52a) integral with a movable clutch member (52) which is slidably but non-rotatably mounted on the transmission shaft (36), the driven teeth being engageable with the drive teeth (37a);
a spring (54; 54A) inserted at a portion thereof into a bore (52b) which is formed in the movable clutch member (52) along the axial length thereof, the spring abutting against the movable clutch member to bias the clutch member to move into a direction of causing the engagement of the driven teeth (52a) with the drive teeth (37a);
a cylinder member (55) fixedly mounted on the transmission shaft (36), the cylinder member being disposed radially inwardly of the drive teeth (37a) and the driven teeth (52a);
a piston (57) slidably fitted in the cylinder member (55), the piston abutting against the movable clutch member (52) so as to move the clutch member into a direction of causing the disengagement of the driven teeth (52a) from the drive teeth (37a); and
a fluid passage (60) formed in the transmission shaft (36) so as to open into an inside of the cylinder member (55), the fluid passage being operable to apply fluid pressure to the piston (57) and to thereby move the piston into the direction of causing the disengagement of the driven teeth (52a) from the drive teeth (37a).
Because the front wheel drive clutch according to the present invention is structured such that the driven teeth (52a) is engaged with the drive teeth (37a) by the biasing force of spring (54; 54A) and is disengaged from the drive teeth by the sliding movement of movable clutch member (52) caused by the action of fluid pressure applied to the piston (57), the clutch is engaged by the action of a spring and is disengaged by the action of fluid pressure. The front wheel drive clutch, which is engaged and disengaged by the engagement and disengagement between the drive teeth (37a) and the driven teeth (52a), is small in the number of parts because of the non-employment of a plurality of frictional elements, so that it can be manufactured inexpensively in spite of the fact that it can be operated lightly by means of a fluid supply system in the same manner as the clutch having a plurality of frictional elements. Because a plurality of frictional elements are not employed, because the cylinder member (55) is fixedly mounted on the transmission shaft (36) at a radially inward location of the drive teeth (37a) and driven teeth (52a), and because the spring (54; 54A) is inserted at a portion thereof into the axial bore (52b) formed in the movable clutch member (52), the front wheel drive clutch according to the present invention can be designed in a compact manner in the axial direction of clutch. Further, because the cylinder member (55) fixedly mounted on the transmission shaft (36) is rotated together with the movable clutch member (52) which is non-rotatably mounted on the transmission shaft and because the piston (57) fitted in the cylinder member (55) is, of course, rotated together with the cylinder member so that relative rotation is not caused between the piston and the cylinder member, there are no members which may cause a damage of seal rings or fluid tightness, so that the durability of clutch is enhanced.
According to a preferred embodiment of the present invention, the transmission shaft (36) extends axially of the tractor and is rotatably supported by a clutch casing (50) which is secured to a bottom wall of a transmission case (48) of the tractor with an opening in the bottom wall being closed by the clutch casing, and the clutch casing (50) is provided with an integral support portion (50a), which is inserted into the transmission casing (48) through the opening (49) and which supports gears (32, 33) for transmitting power to the drive gear (37), and a cover plate (50c) which closes a front end opening (50b) of the clutch casing (50) and which supports a front end portion of the transmission shaft (36). Further, the front end opening (50b) is sized such that the drive gear (37) and the movable clutch member (52) can pass through the front end opening.
According to this structure, the gears (32, 33) for transmitting power to the drive gear (37) need not be supported by a separate support member supported by the transmission case (48) and the gears (32, 33) can be assembled into the transmission case at a same time when the clutch casing (50) is secured to the bottom wall of the transmission case. Further, the front wheel drive clutch can be assembled very easily. That is, the front wheel drive clutch can be assembled onto the transmission shaft (36) at an outside of the clutch casing (50) and, then, the transmission shaft having thereon the front wheel drive clutch is inserted into the clutch casing (50), having been secured to the bottom wall of the transmission case (48) with the gears (32, 33) supported by the support portion (50a), through the front end opening (50b) which permits passing of the drive gear (37) and movable clutch member (52). The assembly of front wheel drive clutch is then completed by securing the cover plate (50c) to the clutch casing so as to close the front end opening (50b).